Email Startups funded by Y Combinator (YC) 2026

Building the communication infrastructure needed for fully autonomous agents

Supafax is an AI agent that lives in your inbox and proactively manages your email and calendar.

AgentMail is the email inbox API for AI agents. It gives agents their own email inboxes, like Gmail does for humans.

AI that helps you fly through your inbox.

Cedar helps the fastest growing GTM teams ramp up new reps faster & spread top rep playbook throughout the team. AE's at Cursor, Corgi, Pylon, and Warp use Cedar to save 75% of admin time on CRM updates, follow-ups, and deal strategy. Backed by YC with an ex-Figma, Notion, and Intuit team, Cedar was built by spending hundreds of hours with the best AE's in industry – we've built a playbook for the fastest growing teams and founders ramping up sales, and we'll use it to automate the busy work so you can sell more, better.

Email sucks. It takes forever to go through, and hiring an assistant is costly and invasive. Friday is building the assistant that learns how to predict the action that you will take on your emails, and does it for you. Today's email products try to help you go through your emails a little faster, but if you have to get through 1000 emails, those products doesn't do much for you. The reality is, most of the emails you get don't require you to personally look at them. Friday completely eliminates the need to check those emails, and handles them all at once for you, immediately. Friday is here to file away spam, sift through newsletters for important tidbits, text you important notifications, and reply to mundane emails, so that no matter how many thousands of emails are in your inbox, you'll just be left with the few emails that actually require your personal touch. Getting this right is difficult, so everyone else settles with trying to help you go through your email twice as fast. If you want to go 100x as fast, you shouldn't spend even a second on useless emails. Friday gets this right, bringing the elite experience of having a professional assistant to the entire world.

Proxis is the AI automation platform built for enterprises. Proxis is creating AI email agents that empower brands and enterprise teams to close deals automatically. Think: your inbox, on autopilot. We initially fine tuned and distilled LLMs for enterprise use—and quickly realized that companies need more than just smarter models. They need full-stack automation. So Proxis built AI agents that handle the tedious, time-consuming work—everything from autonomous sales closers to customer service agents. The mission is bold: to build the world’s most capable team of AI agents for every enterprise. Proxis imagines a future where a single founder can run a billion-dollar company—backed by a custom-built army of agents. Proxis is rethinking how agents are built, trained, and deployed from the ground up.

Zuni is a Chrome extension that gives you AI capabilities in the sidebar of your browser. It can use what it sees on any of your tabs as context, and proactively helps you draft messages and emails.

Odo is your email assistant because you deserve a better morning. Odo can help you organize, draft emails, and follow-up effortlessly after meetings.

Recent changes in email clients made it possible to embed a whole website inside an email. We've built the first email builder that lets Shopify brands create emails that are fully interactive like websites. Zaymo emails decrease friction and increase conversion for product marketing and data collection.

Lightmeter is turn-key email outreach infrastructure for startups, combining network, platform, and expert advice. It integrates with sales tools like Apollo, replacing Google and Microsoft for email delivery. No change in tooling or workflow required. Lightmeter gets mail into inboxes, scalably and sustainably, while transparently reporting on performance. Plans from 50 to 7,500 outreach emails per day.

Loops is a simple and beautiful email sending platform for SaaS companies. We have a Notion-style block editor for email creation, excellent deliverability for transactional mail and pre-built loops for SaaS companies to snap-in to increase their revenue and user engagement.

Waypoint combines a modern email API with a visual template builder so teams can ship faster. Alternative to SendGrid, MailGun, or Postmark.

Compose AI is a free Chrome extension that helps automate your writing using AI. You know how Gmail autocompletes your emails? Compose.ai is like that but everywhere, like how Grammarly works.

Mailwarm is the email deliverability company. We help senders get into the inbox and stay there, through products, tools, and services built for both humans and AI agents. ✦ Mailwarm.com: The original email warmup tool. Build sender reputation automatically through real, positive inbox interactions across a large network of mailboxes, with built-in monitoring and deliverability insights. ✦ ThemailX.com: Instant deliverability diagnostics for AI agents and humans. Check all protocols SPF, DKIM, DMARC, Inbox placement and more via MCP, API, or web. Get specific fixes and actions, not just scores. ✦ Mailadept.com: Email deliverability on autopilot. A subscription-based, AI-native service where agents and deliverability experts collaborate to audit your setup, fix issues, and monitor inbox placement continuously. Build reputation with Mailwarm, diagnose problems with themailX, fix and maintain with mailadept. Doing email marketing or cold outreach? Book a call through mailadept.com, we'll show you which one fits.

MailTime Email Messenger: Mobile email client that makes emails as quick and easy as texting. MailTime AI: Draft and proofread emails using generative AI.

Hive is the industry-best marketing platform for event marketers. Our platform powers marketing for 1500+ of the most iconic event, festivals, venues, promoters, and event-centric brands across North America. We help our clients sell out their shows and make their events unforgettable - by helping them grow their customer base and personalizing and automating their email, SMS, and ad campaigns. Hive integrates with 25+ partners like Ticketmaster and Shopify, ingesting rich customer data in real-time. With this data, event marketers can segment their audiences in powerful ways and send timely, customized messages to their customers.

Polymail is an email platform for sales communication. Our platform - which includes email tracking, Salesforce sync, and calendar scheduling - empowers sales teams to increase conversion and shorten sales cycles while providing executives with transparency into sales activity. Backed by Y Combinator and based in Los Angeles, Polymail has helped thousands of customers transform their sales communication processes. For more information visit http://polymail.io

Posterous emerged from Y Combinator in the summer of 2008 as an innovative company focused on making blogging simple - as simple as sending an email - and now has more than 15 million monthly users. With the launch of Posterous Spaces, the company is bringing its trademark simplicity to help people share smarter with intuitive privacy controls to share selectively across multiple platforms.

ReMail is an email app that downloads all your email to your iPhone and offers a comprehensive email search.

Rapportive shows you everything about your contacts right inside your inbox. You can immediately see what people look like, where they're based, and what they do. You can establish rapport by mentioning shared interests. You can grow your network by connecting on LinkedIn. Imagine relationship management built into your email. For free.

Mailgun is a developer-focused email delivery platform that empowers companies to send, receive, and track transactional and marketing emails through an API. Founded in 2010, Mailgun became a Y-Combinator success story later acquired by Rackspace. In February 2017, Mailgun spun back out as a standalone business focused on building best-in-class email deliverability solutions. We are headquartered in San Antonio with remote teams in San Francisco and Austin. Customers like Slack, Lyft, Github, and Reddit rely on Mailgun to deliver email to their customers.